There is a need particularly in the automotive industry to manufacture parts in a cost effective manner that are generally light-weight in order to reduce fuel consumption in the operation of motor vehicles. One approach to achieve light-weighting is by foaming articles.
It is known that a foamed blow molded article can be manufactured by extruding a plastic containing a blowing agent to form a parison, inserting the foamed parison in a mold and then pressurizing the parison to form an article.
It is also known that a hollow structure can be made that is of multiple layers of substantially constant ratio that may include a foamed layer.
One limitation of the known processes is that the ratio of a foamed layer to its outer skin or to an extruded additional layer is substantially the same throughout the part. The foam layer introduces a structural deficiency at locations such as mounting tabs, at bellows or mounting cuffs in relation to similar entirely solid layered articles. There is a need for a cost effective method to introduce additional solid material at specific locations and to reduce the relative ratio of foamed material at these locations.
Another limitation of the known processes is that foamed plastic cannot be selectively located in areas where it is desired. There is a need to be able to add an increase in foamed material where improvements in acoustic or heat transfer properties are required.
There is a need for a cost effective method to introduce additional solid material at specific locations and to reduce the relative ratio of foamed material at these locations.